function _(selector) {
  return document.querySelectorAll(selector);
}

HTMLElement.prototype.show = function () {
  this.style.display = 'block';
}

HTMLElement.prototype.hide = function () {
  this.style.display = 'none';
}

NodeList.prototype.hover = function (fn1, fn2) {
  for (let i = 0; i < this.length; i++) {
    this[i].onmouseover = function () {
      fn1(this);
    }
    this[i].onmouseout = function () {
      fn2(this);
    }
  }
}